1. Field of the Invention
The invention relates to an extraction device for continuous rolling mills using a retained mandrel. The device substantially comprises at least one rolling frame having three pressure yielding rollers.
2. Description of the Prior Art
When pipes are produced by continuous rolling in rolling-mills using a prior-art retained mandrel a device for extracting the end of each pipe from the tip of the mandrel after the rolling operation is completed has to be placed downstream of the rolling train.
An extraction device widely used at present for the aforementioned purpose comprises a number of three-roller frames which are constructed substantially as a calibrator in order to finish the rolled tubes at the same time as the tubes are extracted.
The rollers in the frames of the aforementioned devices are used for simultaneous extraction and calibration, which means that the rollers perform a reduction operation on each manufactured pipe. In order to perform such reduction work on thin or medium-thickness tubes, the diameter of the orifice defined by the three rollers of each frame in the extraction device must be less than the diameter of the mandrel used in the rolling-mill.
It is known that during the operation of a continuous rolling-mill comprising a retained mandrel, the mandrel may accidentally be disengaged from the securing device, with the result that the mandrel and the rolled pipe therein may move downwards through the entire rolling-mill. When the pipe and mandrel secured thereto enter the first roller frame in the extraction device, they meet an orifice which, as already stated, has a diameter less than the mandrel diameter.
The above-discussed occurrence inevitably results in serious damage to the rollers and/or the associated mechanical parts, which will necessitate prolonged stoppage of the entire plant and replacement of one or more damaged frames, resulting in damage and economic losses.